pro twirl, rotate=rotate, scale=scale, perspective=perspective

@compile_opt.pro		; On error, return to caller

;+
; NAME:
;	twirl
; PURPOSE:
;	Rotating relative to normal coordinates [0.5,0.5,0.5] (center
;	of display rather than the origin [0,0,0]
; CALLING SEQUENCE:
;	twirl, rotate=rotate
; INPUTS:
;	rotate		3 element vector
; PROCEDURE:
;	Translates center to origin, rotates, and translates back to center
; MODIFICATION HISTORY:
;	MAR-2000, Paul Hick (UCSD/CASS; pphick@ucsd.edu)
;-

ddoff = 0.5*[1.,1.,1.]

if n_elements(rotate) ne 3 then rotate = [0,0,0]
if n_elements(scale ) ne 3 then scale  = [1,1,1]
t3d, transl = -ddoff
t3d, rotate = rotate
t3d, scale  = scale
t3d, perspective = perspective
t3d, transl = ddoff

return  &  end